Electrorheological (ER) fluids are novel intelligent material, which are complex fluids comprising dielectric particles mixed with an insulating liquid. Without an external electric field, the ER fluid is in the liquid state; when an external electric field is applied, the shear stress of the ER fluid increases as the electric field increases. When the electric field strength is high enough, the ER fluid may be transformed to a solid-like state. The transformation of the shear stress is reversible, and the response time is within milliseconds. Because of the unique characteristics of the tunable hardness, ER fluids are useful in industry and military fields.
Ordinary metallic electrodes are usually used for the measurement and application of ER fluids as positive and negative electrodes. The conventional ER fluid is based on the polarization interaction between the particles, its shear stress is relatively low, usually no more than 10 kPa, therefore, the ordinary metallic electrodes can basically meet the conditions of the ER fluid interaction and satisfy the requirements for measurement and application of the conventional ER fluid material.
The yield stress of the polar molecule dominated electrorheological (PM-ER) fluid may reach several hundreds kPa or higher, which is tens of times more than that of the conventional ER fluids, and the dynamic shear stress also greatly increases. Usually, ordinary metallic electrodes can not meet the orientation and conditions of interactions required for the polar molecules, and the ER fluid and the surface of the electrode may “slide.” Therefore, if ordinary metallic electrodes are used, the shear stress of the ER fluid is much lower than what can be actually achieved, which greatly restrain the application of the PM-ER fluid. The use of the surface roughening of the electrodes may ease the problem of “slide” such that the shear stress as measured may increase about twice, however, the treatment makes the rough surface of the metallic electrodes easier to electrically discharge, and difficult for the application in a high electric field.